The Instrument She Plays
by IShouldBeOverThis
Summary: Mycroft says that Sherlock must solve a problem of global importance.  REALLY, REALLY need feedback on this-first real mystery.  Please don't make me beg.  I think it's a good premise. Don't own: yada, yada.


There was a woman's voice coming down the stairs of 221b which probably meant that Sherlock had a case and John didn't like interrupting Sherlock when he was listening to potential clients.

If the voice had sounded low, rich and attractive coming up the stairs, it was nothing compared to the woman who was speaking, and John couldn't help stopping outside the door to the sitting room.

It didn't take the deductive abilities of the world's only consulting detective to see the family resemblance. Sherlock was leaning against the table while the woman perched on the arm of Sherlock's chair, their long legs stretched out similarly. She was as long and lean as Sherlock, and dressed likewise in a slim-cut, black suit. Her shirt was emerald green, tightly seamed across the front like a corset, and it suited her pale skin just as Sherlock's purple shirt suited him.

But it was the face that gave it away. It was less long and narrow than Sherlock's but with the same sharp cheekbones, the sculptured planes of the cheek tapering down to a narrow chin that gave her face a heart shape. Her lips matched Sherlock's in their fullness and bow shape but hers were crimson with lipstick. Her eyes were more round, but they retained the same cat-like slant of both Sherlock and Mycroft. They were more green than Sherlock's but still silvery like foam on the ocean. Somehow the pieces shouldn't have been beautiful—her eyes were too far apart, her mouth was too big for her face—but added together, she was striking. The only flaw was her nose which was a little too long and down-turned with a fullness around the nostrils that echoed Mycroft's. Her hair was as black and as soft looking as Sherlock's but completely straight, pulled back into a loose bun with chopsticks, with a thick fringe and long, loose strands geometrically framing her face.

She glanced up at John and smiled—one of those slightly fake smiles that the Holmes family seemed to have down pat—and arched a perfectly plucked eyebrow. Her stare was as mesmerizing and penetrating as Sherlock's. John felt like a bug under a microscope.

"You must be John," she said striding across the room with her arm extended to take his. Yes, the same long white fingers. She was wearing three inch heels which made her as tall as Sherlock and made John feel like a dwarf. "Sherlock, are you going to behave yourself and introduce us?" Her accent was interesting. As richly modulated as Sherlock and Mycroft, and just as plumy, but the vowels were slightly flatter somehow.

John finally tore his eyes away from her just in time to see Sherlock's scowl.

Reluctantly Sherlock said, "John, this is my sister, Halwell. Halwell, this is my friend, John Watson."

"Delighted, John. I've heard so much about you."

"Really? I've heard absolutely nothing about you."

She laughed, and unlike either Mycroft or Sherlock it was a genuine and deep-throated laugh. John felt his stomach lurch a little.

"Oh, that is so like them, isn't it? Mycroft playing 'need to know only' and Sherlock, well, Sherlock has never liked to share. Many toys ended up destroyed rather than let Mycroft or I have a chance with them."

Sherlock's scowl deepened. "Mycroft was too old for my toys, and you tended to break mine before I got to them."

She tilted her head slightly and closed her eyes, but whether it was in acquiescence or in dismissal John wasn't sure. "Really, Sherlock, how old are we now? You're still resentful?

"I've heard about you from Mycroft, John. Sherlock doesn't communicate with me very much. Can't imagine why. I absolutely adore him," she smiled over her shoulder, "Oh, and the mixed accent comes from living in America for many years, too many years."

John wondered how she knew that he'd been wondering, but knew better than to ask. That was the Holmes family apparently. Did family trips consist of the three of them (or were there more, unmentioned until they popped up) out deducing each other?

"My sister runs the New York stock exchange."

"Oh, now Sherlock, you exaggerate! I suppose he told you that Mycroft IS the British Government. I am a consultant to the major trading firms. I deal in the probability of market trends, in cause and effect.

If I WERE in charge, we wouldn't have had that nasty little problem two years ago, I can tell you that! Although I did warn them back in 2004. Well, really for most of the 90's. All those funds and products they were setting up—I told them it was like people who put something in what they think is a very safe place only to forget where they put it when they need it. Silly men wanting bigger toys. It should never be about the toys."

She strode back to Sherlock on her long legs. "Good-bye, little brother. Please consider what I've offered. I think it's worth your while." She leant in for a kiss and a small hug which Sherlock surprisingly reciprocated with intensity as if he were reluctant to let her go.

"John!" she whirled about, breaking from Sherlock's grasp, "Sherlock is busy pondering a mystery. Why don't you and I have dinner together and I can answer all the questions you're dying to ask? I'm staying at Claridges. Really just around the corner. I'm sure you want to refresh yourself after working all day and I want to get settled. Meet me in the restaurant say in an hour and a half? Oh, and don't worry—it's all on expense account so neither of us has to think about the bill.

"TTFN, Sherlock."

And she was gone leaving a swirl of light florals and spice in her wake.

John looked back at Sherlock. "Bloody hell, Sherlock. When were you going to tell me about her? Any others I should know about who might come strolling back into our lives?"

"No, you've met both of my siblings now. She lives in New York. She never comes home. It seemed unlikely that you would ever need to meet her."

"But she's your sister! Most people mention that they have siblings, even if they're estranged."

"John," Sherlock looked at him hard for a moment. "John, if I had not deduced that you had a sibling on that first night, how soon would you have told me about her?"

John pondered that one for a moment. "Not immediately, but before now. Is your sister an alcoholic?" John paused, "A drug addict?"

"No, although I think she might have used coke for a bit in the 90's. Mycroft would know better than I. She's certainly clean now. No, she's…she's dangerous, John. I can't explain how or why right now. She's very manipulative."

"Oh, yes? And you and Mycroft are the souls of courtesy!" pause, "Do you not want me to go to dinner?"

"No, by all means go. She is very charming and she will answer your questions. Just be careful. That's all I can say." Sherlock sat down at his laptop signifying that the conversation was at an end.

John shrugged and went upstairs to have a shower and change. There was no point in asking Sherlock anything more. It was going to be an interesting night. He wondered if he had anything that could remotely fit in at Claridges.

At seven o'clock John entered the grand entranceway of Claridges, with its elegant art deco design. Yes, despite his jacket and tie he was definitely underdressed.

She seemed to uncoil from her bar stool when he entered. She had changed to a white gown that was folded around her in a strange origami that was both figure flattering and angular. There was a thin red edge around the neckline to separate the milky skin from the cool white of the dress.

They were seated immediately at a table near the window. John was a little boggled about how the staff seemed to be ready to cater to her every whim.

Wine was ordered and after some slight consideration, lobster for both of them.

"Now, John, tell me what you want to know. I know neither of my brothers has willingly volunteered anything about our family. It's not their way—read everyone else, but hold people who can't do that in contempt. But not you? They both like and even admire you." She said the last as though she were describing someone's fondness for a slightly mangy dog.

"All right," John dove in, "are you and Sherlock twins?"

"Easy one. No, we are, what used to be called in a more racist time, Irish Twins. I am 12 months and 13 days older than he is. I really can't imagine how Mummy and Daddy were so sloppy. I mean, six years between Mycroft and myself, and barely more than a year between Sherlock and me?"

"What's with the names?"

She laughed again—that amazing laugh that caused not a few glances and then smiles at other tables. It was infectious.

"Oh, they are old family names. They're probably in the Domesday Book—some bits of Saxon, bits of Norman and probably even some Norse. The English language is endlessly fascinating, don't you find? Our poor father is saddled with Pemberlane if you can imagine. He goes by P. R."

"R?"

"Richard."

"And yet none of you goes by your middle names or your initials when it might be easier."

She shrugged. "The three of us revel in our uniqueness, our separateness, I suppose."

"Your middle names—are they equally strange?"

"Mycroft William, Sherlock Edward and Halwell Elizabeth. How plebian!"

"Mother's name?"

"Really, John. Let's move on to the really juicy stuff. I feel as though I'm filling out a medical survey. Isabelle Louise nee Simpson."

"I can't imagine any of you as children. I really can't. What was it like? Are your parents brilliant?"

"Daddy is a scientist. Or was, he's retired now. He worked on top secret things for the military in the 70's. I honestly don't know what he did. Official secrets and all that. Physics and some chemistry. Mummy taught modern languages at a comprehensive until she married. After that she painted. Still does.

"Our childhood was really very normal. Well, we were very bright, as you can imagine. Rather competitive. Fairly destructive from being endlessly curious. Had a lovely Old English sheepdog named Magus and two wire-haired fox terriers named Boxer and Daisy who we treated rather better than you might expect. We were very ordinary, really. We went to movies, read books, watched Doctor Who and fell down and scraped our knees. That is a lie, of course, we were bored at movies, read research books and analyzed the science of Doctor Who. We did scrape our knees and generally got ourselves hurt more often than not—what with experiments and other things."

She looked off into the middle distance for a moment. "It was hardest on Sherlock, I suppose. Mycroft learned to be ingratiating early on. It's easier for girls. Girls can be monstrously cruel of course, but not for the same things. Not for your name or your smarts as long as you don't lord it over them and are willing to do some class work for them.

"Sherlock has that obstinacy that he mistakes for an ethic. He was all gangly limbs and lovely bones even then, and inadvertently dismissive and cutting without really understanding that he was. He was called Shirley a lot," she laughed. "I was Hal as a toddler, because it's what he called me. I called him Sure, which everyone thought terribly funny. We called Mycroft My forever—even after we knew better because it annoyed him so. I tried Hal on again as a teenager—trying to be tough, but it didn't stick. And can you imagine Mycroft being called Mike or Mikey?"

John laughed, "No, can't really. So, about you. What does a dealer in probability do?"

She looked at him again with that penetrating gaze. "Do you know what it's like in our minds, John? Mycroft and Sherlock and me, I mean."

John wasn't sure that he wanted to know.

"It's like everyone else in the world is playing board games and we're playing with a three-dimensional geometric puzzle. We can hold things up in our minds and turn them all around, from top and bottom and 360 degrees. Move it around, manipulate it, pull bits out and slot them in elsewhere. Mycroft does it with politics and government information. Sherlock does it with criminals and crime. I do it with mathematical and social probability.

"Will the market jump this way or that, and what can we do to maximize our profits. I have to look 20, 30, even 50 years down the line. What will this product do when this generation comes of age? What is its shelf-life? What kind of profit or loss will it make for the company depending on the direction of the market, and even whether the laws will change and it will be deemed a sort of fraud at some future date. I write algorithms for computers to keep churning out that kind of data. I also do some of it in my head.

"Of course, the wetware problem is unavoidable and unpredictable."

"Wetware?"

"It's a slang for the human element. The piece that can be predicted in broad terms, but not in the detail. The odds say that most humans will behave this way in a certain situation, but there's always some sod who will jump the other way. Panic in a non-panic situation. Grab or ditch when he should be yielding or holding. Did you know that most people will go right when entering a store? Most stores will put their check-out at the left if at all possible so that people reach it only after walking around the whole store in a counter-clockwise direction. However, you'll always crash into someone going the other direction.

"Probability can only ever really determine the odds of one thing happening at a time. You roll a pair of dice. There is a one in six chance that the first die will be a six. There is a one in six chance that the second die will be a six. They are independent of each other. It isn't like the dice are connected, that IF the first die is a six, then the odds of the second being a six change. Still one in six, but the odds of both being a six grow exponentially, so the odds are one in 36. And so on, with more and more data—the odds against grow and grow. And if you track the odds you start to see broad patterns in the numbers of times that you will roll a double six. But in the end, it's just your hand, rolling the dice, with a little more force this time, a little less next, fumbling them in your hand for a moment and so on. Mandelbrot, who just died, pointed out that there is always a piece of the random in everything. Chaos and entropy will always win.

"By developing ever tighter and tighter algorithms, I try to minimize the wetware effect, stave off the chaos for another day. And remember, the house wins. It's my job to make sure that they win.

"That was probably more than you wanted to know."

"Um, vaguely remember probability and basic economics from school. Like how to balance your checkbook," he laughed and she laughed again. He was beginning to really enjoy that laugh.

"I don't really know how Mycroft does it. All his variables are wetware—predicting where the next crisis will be, estimating the effect of a dictator coming to power—years in advance—like Hussein, or even the 'good guys' like Obama or Cameron and Clegg. Of course, he also gets to manage it more than I do—move the players around. I'm stuck with the dick heads that broke the machine. It's such a burn-out industry. Just when I've got one group trained, they make their billion and take off and I've got a new bunch on my hands who think that they know it all."

"Do you invest in the market—since you see it behind the scenes as it were?"

"You really are quite remarkable. The boys are right. That was an unexpected—unpredictable—thing to say."

John felt a slow flush creeping up his cheeks, "Why, what would most people say?"

"Can you make me any money?"

They laughed again together. And John thought that Sherlock might be a wee bit jealous of this fascinating woman who seemed to be able to move in society without scaring people."

"Sherlock thinks he plays with facts, but in reality he's playing probability too. A slight guesswork extrapolated from the available information that tells him who people are and what a criminal might do next. His powers of observation are remarkable, what he absorbs without even knowing it.

"He's very good at guessing, which makes it seem like fact.

"Take, for instance, this room. Most people in this room think that we're a couple. They hear me laugh, and see you smile, and think, 'Oh, they're in love,' or more crudely, 'someone's getting lucky tonight.'"

John flushed again.

"If they observed," she continued, "they would see that we are relaxed in our posture, leaning back in our chairs, not sitting alert to one another's bodies, leaning in together."

She leaned in. "Now, if I were to lightly touch your wrist like this, or laugh after something you've said, rather than at my own voice, they might have something."

John swallowed hard. "Um, I don't really like to be experimented on."

"Who's experimenting, John? You are really quite adorable, if you don't mind my saying so, but with a hard-tempered edge that is…stimulating. And I've already complimented your mind.

"You are playing a harder board game than other people. Pente perhaps, maybe basic Go. Something that takes strategy. You aren't living by random chance. You are the intriguing wetware in the machine that is my brother."

"We're not a couple!"

"I didn't say that you were. I wouldn't be doing this," her fingers lazily traced circles on the back of John's hand, "if you were." He became aware of her foot touching his leg.

"I don't really take his toys just to take them. And I know you're not a toy." She smiled lazily at him, that sideways smirk of Sherlock's and Mycroft's but more relaxed. Her eyes were just as piercing. This time John felt she was looking into his soul.

"Room 413, John."

"What?"

"That's the room I'm in. Would you like to see it? It has a lovely view."

They crashed together inside the room, mouths meeting as she kicked off her shoes to better even out the height." She was still taller, but not as tall as Sherlock. John didn't have to look up at her or reach to meet her lips.

She pulled him into the room, to the turned down bed. She was forceful, fumbling a condom from her bag and putting it on him. It had a striking intensity. Nothing like the slow, normal pace he'd had with Sarah or any other woman, for that matter. It was, if he'd imagined such things, exactly how one would expect a Holmes to be in bed. She told him what she wanted in no uncertain terms and read what he needed, pausing only occasionally to confirm her guess. She was all slim limbs and smooth plains, with only the slightest curve to her hips and a gentle swell of breasts.

He woke in the morning, bleary eyed, to the smell of breakfast and the sound of a hairdryer. Halwell came out of the bathroom clipping her hair up in a much more severe bun than she'd worn the day before. Breakfast was on a trolley under silver domes.

"Sorry, John, have to dash to a meeting. Sorry to kiss and leave, as it were. Have some breakfast." She lifted a lid, grabbed a single piece of toast, ate it quickly and downed a cup of coffee like it was a shot.

"I'm not an ersatz version, John. I'm the real thing. And I won't take second place. X does not equal y."

John was left pondering that enigmatic statement as she swept out the door in the same light, exotic scent as the night before.

John showered with the hotel amenities and got dressed. Somewhere in the night she'd sent his clothes out to be cleaned. His shoes were even polished. They must have brought them in with breakfast. So this was what a luxury hotel was like. This could be fun. He wondered, not for the first time, why Sherlock was slumming it.

When he entered the flat he found Sherlock in the same clothes still perched over his laptop, fingers templed.

"So she seduced you, did she?"

"Well, I wouldn't call it that," John felt distinctly embarrassed. It was always strange to date/shag your friend's sister. "I mean she's lovely, really lovely, and we had a good time."

"I'm not going to ask you what your intentions are towards my sister, John, if that's what you're worried about. No, I'd be much more likely to ask what her intentions are towards you," he smirked a little at that, damn him.

John felt vaguely uneasy. Was he just some pawn between two Holmes siblings again?

"Sherlock," he asked, settling himself in his chair. "What did she offer you yesterday?"

"A puzzle. She says that there's a serious flaw in the security systems of the London Stock Exchange."

"So you'd be paid to find it?"

"Yes, John, the rent would once again be safe. But I don't know. She plays games as much as Mycroft. There's something else here that I can't put my finger on."

John shut his eyes for a moment. He realized that he hadn't asked Halwell a vital question: why the Holmes siblings were so embattled.

"What did you mean when you said she was dangerous?"

Sherlock paused with his eyes downcast for a moment. He moved abruptly to his chair and faced John squarely. Never a good sign.

"She didn't tell you how she ended up in America, then. No? I rather thought she wouldn't.

"When she was young she was a fire starter, John. No one got hurt, well one person and that was a minor accident although I doubt he ever got the full use of his hand back. He simply walked into the experiment at the wrong time. I don't think she ever meant to hurt anyone, although I'm not sure…

"Do you know the term, 'Cat's paw?'"

"Isn't it from some story about a monkey tricking a cat into burning itself, by Kipling or something? Oh…" John paused, a slow realization dawning.

"LaFontaine, actually, but I am impressed with your deduction. Yes, it was never her hands that lit the match. She always rigged it so that someone else did it for her. At first it was purely mechanical. Fires that could be started by contraptions that someone might accidently set off. That was from about eight to ten. As she got older, she decided that psychologically tricking people into starting them was better. She was, and is, interested in what she called the Human Uncertainty Principle."

"Wetware," sighed John.

"Yes, she started calling it that as she got more into the coding, into the computers and the systems.

"When she was fifteen she burned down our gazebo. She sat and watched it burn. Mummy and Daddy weren't home, but I saw her sitting there on the lawn, just watching.

"Mycroft stepped in at that point. We'd always known about it, and she never tried it on us. She would boast of her achievements to us—how this had triggered this, which led to this and voila—but we all did that for each other. There was no one else to tell.

"Mycroft stepped in and told our parents. Laid everything out. He said that he'd only just reasoned it. That being away at college had made the coincidences more clear to him.

"She was sent to a boarding school, well, luxury reformatory, in upstate New York. It was the only one that specialized in that sort of discipline, at the same time providing a quality of education and a discretion that ensured that her future prospects were not imperiled. She wouldn't be in finance now if her employers knew about that.

I will never forgive Mycroft for that hypocritical betrayal, and she will never forgive me for not using my skills to prove to Mummy and Daddy that she was innocent, for not protecting her from everyone else."

John was a little staggered. That was a huge issue, not a petty feud between Mycroft and Sherlock.

"Thank you for telling me," he said at last, his eyes meeting his friends and seeing a sorrow there that he'd never thought he'd see.

"Please don't tell Mycroft or Halwell that I told you."

"I never would."

"I know, John," Sherlock smiled weakly.

"Why did you let me go with her? You probably-," he almost said guessed but caught himself, "—deduced what would happen." Now it was John's turn to sound a little hurt.

"I have learned that the more one forbids my sister, the more she wants it. It seemed logical to let her get you out of her system. And her out of yours. I wasn't playing with you, and I suppose, if it helps, neither was she. We all have our addictions."

The day passed slowly. John kept wondering if she would call and wondering what he would do if she did. Sherlock was working out some mystery that didn't require an onsite investigation, but did require some internet research. Around dusk he cried, "A-ha! It _was _accidental. If he'd understood the rate of release it would have worked on the intended victim, his uncle, as payback for the abuse. That's why he was able to be so grief stricken in the police interview. He was." He typed rapidly on his mobile for a moment.

John actually made dinner rather than ordering in—something simple, pasta and bruscheta—and they settled in to watch the telly.

"We interrupt this broadcast to bring you breaking news of an explosion in Harris Street in the Bethnel Green area. First reports indicate that it may be a gas main break, but the police are not ruling out the possibility of a deliberate attack."

Sherlock studied the screen behind the reporter with his strange intensity. He rapidly flicked through the other stations that were just reporting the accident, pausing only momentarily on the ones that were showing the street.

"Phone, John!"

There was something so urgent in his voice that John didn't hesitate to toss him his.

He texted furiously for a moment.

**Lestrade,**

**It's not a gas main explosion. It's deliberate, but I don't think it's terrorists. I need access to the whole block.**

Moments later the phone rang.

"Lestrade. Can I come? Is the bomb squad swarming over everything?

"Fine, fine. I need access to the other buildings, not the one that blew up.

"Coming John?"

"Of course. Should I bring the gun?"

"I don't think so, not yet, at least."

In the cab John turned to him and asked, "So, not taking the paying one your sister offered, but doing this for free?"

"Hers is boring. This is something, something big."

John thought that eating and paying utilities was not boring, but didn't say it aloud. Sherlock was too busy studying his Google maps to talk.

The street was full of emergency workers, police and firemen. Lestrade and team stood by the cordoned area organizing the teams.

And there was one surprising figure, standing next to his Bentley, umbrella in hand.

"Mycroft? Are you here because Halwell is in town? Have you spoken to her?"

"Yes. Well, we spoke on the phone. You know that she prefers not to actually see me. While you she will see, but not communicate with. Curious? I know what she has asked you to do.

Sherlock, you must do what she asks. It is of national importance. More, of global importance." He glanced at the shattered block and Sherlock followed his gaze. For a moment they looked so alike—an almost greedy look in their eyes. "Now, more than ever."

Inwardly John groaned. If there was one sure way to make sure that Sherlock didn't take the case, it was to tell him that a) it was important, and b) that it was important to Mycroft.

"I have a case. This one is quite fascinating."

Mycroft turned to survey the street again. "Yes, you solve this one," he said thoughtfully, "then we can talk again." He nodded again, seeming to lose interest in the conversation, got in his car and sped away.

Well, that was odd, thought John. To not insist; in fact, to encourage Sherlock to take this case, whatever it might be. Sherlock was already off, examining the buildings around the bomb site with all his usual manic precision.

Harris Street was a very ordinary London block. About six two story buildings backed with an access alley and about four buildings along the other side, Noe Street. The block seemed singularly depressed with no shops open. The one next to the explosion had a 'To Let' sign in the window. The one on the other side was simply boarded up. There was one that claimed to be under construction, but the signage looked old and the wall was covered in playbills. John followed Sherlock around to the other side which seemed similarly empty of businesses, except for one small bookshop and a Laundromat. The bookstore was closed, hours from nine until five, apparently. The Laundromat was open, but devoid of business with one multi-pierced, bored looking young woman manning it. Sherlock strode in, flashed one of his Lestrade badges and began to examine each machine, poking his head in each of the lower dryers and even seemed on the verge of climbing into the multi-load spin machines.

"Is there a back room?" he challenged the young woman.

She couldn't even be bothered to reply, simply waving vaguely towards the back. John followed Sherlock into the one tiny office with an even tinier loo beyond. Sherlock was on the floor again, crawling on hands and knees into the loo. John resolved to make Sherlock wear a mask as well as gloves next time. There was a safe set into the floor which Sherlock quickly discovered. It was on a timer, but was very poorly protected in John's opinion. Sherlock growled in frustration.

His next course of action was to stride down the alley, checking back doors. None offered him access. He was even peering down the drains.

"I will have to come back tomorrow," he declared finally, riding home in silence and when home collapsing on the couch with three patches.

John had work the next morning. When he got up Sherlock was at his laptop, well, John's laptop. There was no point even debating it at this point.

The text came in around noon.

**Pick up package at copyshop on way home.**

**SH**

Going to the copyshop took him through the park. And suddenly Halwell was there next to him. She was dressed simply this time. Black trousers and a black turtleneck. Her hair was pulled back in a simple ponytail and she wore no make-up which made her look fragile and young. Her resemblance to Sherlock was striking. She looked tired.

"Evening, John."

"Hello, Halwell." There was that strange awkwardness of running into someone you've had sex with but have no expectation or even desire to sleep with again. John found himself startled at that last. Sherlock's story had made him wary and also sorry for Halwell.

"Sit with me a minute. I love the park at this time of night. I used to come here when I was young.

"Is Sherlock working on my problem?"

"Well, he's considering it…"

"Don't lie, John. My bosses are very eager to know the results. Try to encourage him if you can.

"To live in the world one must be aware of everything, you know, John," she continued. She sounded like she was continuing some of the discussion from the previous night, but rather than sounding excited she sounded almost regretful.

"The three of us, we notice everything, even if we don't realize it. I know Sherlock thinks his mind is a hard drive that he keeps pure, but he forgets that hard drives are constantly writing little files of data. Start-up files, back-up files, temp files. Fragmenting information. Can you de-frag a brain? Can you clear the cache?

"Sometimes I know something and I don't know why I know it. I close my eyes and I see all those ticker symbols running up and down like in The Matrix only mine are in vivid color, a different hex color for every one, thousands upon thousands, and I see their history, when they were high, when they were low. I see their class and their rating and one little one down in the corner will grab my attention, a little shining blue one, not even that important, and I won't know why it's vital, but I know that it is. And finally I'll realize that I saw some article on the CEO months before and realize that he was wearing a tie in that color and that the article was about something in his company—something that has the potential to change everything.

"Sometimes I would give anything not to have all that in my brain all the time. To just turn off, do something mundane and focused, like some old manuscript illuminator. The colors controlled, the words the same every time.

"And then I think, what if it all exploded? Would any of us be able to function? Would the colors overwhelm everything? And then I think of this park, and sitting on a bench holding Sherlock's hand, watching Mycroft fly a red kite. The pine green of the park, the scarlet of the kite, the navy of Mycroft's jacket and shorts. The cotton candy pink of my poncho and Sherlock in a striped shirt like Bert and Ernie, all reds, oranges and browns. And it's so simple and clean, and it's just us, just us against the world.

"You are so reassuringly beige, John, and I mean that as a complement. It's grounding when we are drowning in color... I should go. I'm late for something already." She leant in and kissed him like a sister, as if she had adopted him into their strange world.

The package at the copyshop was a long tube. John paid and headed home with the awkward package under his arm.

It contained blueprints and council maps which Sherlock spread across the floor. John realized it was the Harris Street buildings. Sherlock moved between the blueprints and the maps with a drafting compass, comparing rooms in buildings with their layout on the maps, making small notes in the margins. It was the most annotation John had ever seen Sherlock perform while working on a case. Normally it was all in his brain.

John ate, offered some to Sherlock, was ignored and found himself dozing on the couch with a book, turning on the telly was impossible while Sherlock was working this intently on a case. Suddenly Sherlock cried out as if in pain.

"Why, why, why!" he cried. "Why both of them at once? It's just where I thought it was, but how do they access it?

"John, we have to see Mycroft."

"What!" That was absolutely unprecedented.

"Bring your gun."

Within minutes Sherlock had bundled both of them into their coats and was down on the screen waving frantically at the CCTV cameras. And five minutes later a sleek car pulled up to the curb. This time there was no Anthea and they were taken directly to Mycroft's office, where Mycroft still sat, despite the late hour.

Sherlock wasted no time, "Mycroft, what is under that block? Is it what I think it is?" Sherlock was leaning over the desk, right in his brother's face and even Mycroft looked startled.

"Yes. Yes, it is."

"And you couldn't tell me this yesterday? You let me waste all this time. It's happening tonight. It must be. It will happen at 3 am and you've let it go on. That's three hours away. We might have prevented it."

"It wasn't my secret to tell, Sherlock. Despite everything, the banks are still independent. We know where they are for security reasons, but it doesn't fall under our jurisdiction. Not even 5, let alone 6.

"I haven't been entirely idle. I've threatened bank managers and security for the Exchange. They'll be joining us here shortly. You know I do that better than you and I know that you've found the access point better than I could have. Legwork, after all."

"But you could have told me! She could have told me. I thought she meant the Exchange itself. I even went there today to look around quickly."

"You've found the access point, I take it."

"Of course. It must be at the back of the bookstore, but I couldn't get a good enough look at it today. Damn the store owner. I should have known. One of the team, no doubt."

"I will send men at once to guard it. We have to catch these people, Sherlock. They cannot be allowed to escape. They know far too much."

"You know that they are probably already inside?"

"Certainly. But as you said, nothing can happen until 3 am, although I suspect it can be set up in advance, and depending on how good they are, we may need some time to work."

Sherlock ran his hands through his unruly hair and paced the room.

After about fifteen minutes two men were led in. They looked as John would expect bank managers to look, reeking of wealth but they also looked shaken. John had followed almost nothing of the brother's exchange. Too much left out, but he knew them too well to try and get an explanation right now.

"You're sure?" the first man asked, panic in his voice.

The brothers looked at each other. "Absolutely," replied Mycroft.

The man placed a laptop on Mycroft's desk and opened it. It revealed a three-dimensional diagram of a square room which seemed to be entirely banded in red lines. Sherlock moved in without even asking and started moving the cube around, his fleet fingers moving over the keys and the thumb pad at an alarming speed.

"There," he suddenly cried, pointing at one tiny corner that seemed to be slightly free of the red lines, one tiny spot.

"Oh, God," said the second man as if his life depended on it, which possibly it did.

"They'll have to have come in under it. The explosion was probably to hide the final excavation.

They all looked at each other for a beat and then Mycroft pushed a button on his desk.

"The cars are waiting and the teams. Let's go."

John rode with Mycroft and Sherlock, leaving the other men in another car. Both brothers were hunched with a tension that was out of character and very frightening. Whatever was going on it was enormous.

They arrived at Harris Street to find the book store already broken into, men at the back tearing down shelving and knocking on the walls and the floor with sensor devices.

"I think we've found it sir, but it's solid concrete. However they got in there, it wasn't through here."

John looked around but Sherlock was gone. He scanned the street, and on a hunch ran to the alley in time to see the long coat disappear over a roof. Frantic for his friend but unable to reach the fire escape he was forced to return to the front where Mycroft's men were busy breaking down the wall.

It seemed to take ages and John was almost shaking out of his skin when they finally burst through. Behind the wall was a tiny alcove with a stair leading down. John barely registered what he was doing before he was elbowing the men out of the way to rush down the stair. He was startled to feel a draft and realized that the alcove was open above his head, presumably to on of the air vents on the roof. That meant that Sherlock was already down the stairs.

John dashed down the stairs and stumbled into a small room brightly lit with emergency workman's lighting.

Halwell was sitting on the edge of the hole in the concrete floor. She was covered in dust and there was blood on her hands and her face.

Sherlock stood immobile and dusty, John's gun aimed at her head.

"Shoot me if you're going to, baby brother. It's too boring just sitting here."

Mycroft burst into the room with his men. He looked as close to disheveled as John had ever seen him. "HAVE YOU DONE IT?" he shouted at Halwell.

"No, the cavalry arrives in the nick of time. You have," she glanced at her watch, "Two minutes and forty-two seconds to figure out how to stop it though. I'd get your minions on it ASAP.

Figures in black pulled her away from the hole in the floor and others rushed to drop down into it. At last Sherlock's arm fell to his side. John slipped up beside him and pulled it from his hand, clicked the safety and tucked it into his pants.

"Why?" Sherlock whispered, cocking his head to one side and John could see his eyes were moist.

"FOR THE THRILL! To not be bored, bored, bored. It's hotter than coke and sweeter than heroin. It's like a thousand orgasms at once, but you wouldn't know about that, would you?" she smirked. John realized she was actually insane. It glistened in her eyes.

"Why do you think Mycroft does it? For the thrill. Don't you, Mycroft? Although you deny it. You could have been the best of us, Sherlock—a criminal mastermind—but you didn't. The two of you, wanting to be _good_," she spat out the last word. We could have ruled the world, we three."

Mycroft looked at her, "You know that the chaos that would follow this would create a bloodbath?" said Mycroft, his voice steely and steady once more. John realized that Mycroft had moved to his brother's side.

"People will kill each other and people will kill themselves and the unpredictable ones won't. It's not as if I'm pulling the trigger. Sherlock, you've almost let John die numerous times, and don't tell me that everyone has lived under your watch. We both know that's not true. How many men have you killed, John?"

"And Mycroft," she laughed, still rich, but with that mirthless undertone, "I could kill a person a day until 2514 by my calculations before I'd reach the blood that's on you hands. You destabilize regions! And you excuse it in the name of realpolitik.

"It might be chaos, but it wouldn't be dull for anyone, least of all us."

"Why?" Sherlock asked again. "Why put me on your trail?"

A dark clad head popped up out of the hole, "We've got it, sir. The security is back in place and the worm removed."

Mycroft said, "The whole system must be searched, every last database, motherboard and line of code. I doubt that we have gotten away so easily."

"If I swear that I haven't planted a long acting worm, will you believe me, Mycroft?" she asked, eyes wide and innocent, like Sherlock when he was acting. "Well, there may be something, but I found out about the change too late to really write anything good, so the markets are safe for another day."

Then she flicked her eyes sharply back to Sherlock and they were frenzied again, "Why? For the game, of course! You used to beat me at chess. Do you remember? I wanted to see if I'd gotten better."

"Did you cause the recession?"

"No. That was wetware, pure and simple. Faster and faster machines that move beyond their idiot minds. Really, do you think I bankrupted nations, created the PIGS? That's really more up Mycroft's alley.

"No, but it gave me the idea. May 6th, now that was me. A trial run, if you will. Fun, wasn't it? And it was nothing compared to what would have happened when the markets opened tomorrow. The London Stock Exchange just announced it has the fastest trading algorithm yet. And Hong Kong's launching it tomorrow, well, today. I just had to come over and play with it, now didn't I?

"You really should thank me, boys."

"Thank you?" gasped Sherlock, "for what?"

"Mycroft would have really had some things to manage, and you would have had so much fun crime to play with. Think of it as my gift to both of you for my lovely education at Stonehaven."

"I wrote you every day. I wanted to hear if you were happy? I still loved you so much," Sherlock said, and this time he couldn't keep the sob out of his voice.

"You wrote me that you were miserable at Harrow, Sherlock, as if that was supposed to make my life more bearable. You were at fucking Harrrow! You could go home, walk away, roam the countryside. You probably could have gone home for good if you wanted. I was in prison!

"I wasn't allowed mirrors for fear I'd use them to start fires. I had to ask for someone to be with me so I could comb my hair! I couldn't be left alone to shower, for fear I would do something to the water system. I was under watch every minute of every day! And I was in with girls who were genuinely dangerous, genuinely psychopathic with no empathy whatsoever. And the matrons. Lovely, lovely concerned women, who were just that little bit sadistic to the girl who knew their every thought."

"Spare me your love, Sherlock. Spare me your concern, Mycroft. We all chose our sides a long time ago.

"Can we get out of here? This conversation is beginning to tire me."

"Check her mouth and her clothing," said Mycroft coldly. "She's very talented at escape. We used to play Houdini.

"And the others?" he asked before he turned to go, "You're assistants?"

"Brute force, nothing more. I told them I was robbing an old abandoned bank vault and that money would be wired to accounts. Which it was, but it really wouldn't matter after tomorrow."

John, Mycroft and Sherlock walked out into the night air. Both brothers looked as though they might collapse at any moment.

"I'm sorry," said John, almost more to give them something to focus on, than from genuine interest "I know I'm thick, but can you explain exactly what she was doing?"

"The servers, John. She asked me to find the weakness in the security system of the London Stock Exchange. I thought she meant the building itself, but she meant the back-up servers. They're never kept at the actual location of the bank; a terrorist could blow up the bank and destroy all the records of transactions. There's always a secret location where everything is backed up at 1 second intervals, and even that is considered desperately slow in this day and age. That's why the collapse of the American towers didn't disrupt the markets of the world, well not directly. The servers for all those financial companies was housed somewhere else.

"The bunker that houses the servers has sensors on all sides, top and bottom, six-sided like a die, but she found one little corner that was accessible, that would let her access the security system and shut it down for exactly four minutes. Then the back-up security would kick in. During that time she hacked into the servers and planted a worm that would disrupt the trading algorithms. As of last week, the London Stock Exchange has the fastest one in the world. It trades at 124 microseconds, and Hong Kong is converting to it tomorrow. I'm not exactly sure what the worm would have done, melt down the servers, block trades, I don't know."

"It would have disrupted that speed," continued Mycroft. "It was to throw a randomizer into the works, so that some trades would go through at that speed, but others would go through slower, hoping from one firm to another. There would be mass panic as the markets fluctuated wildly. On May 6th the American Stock Exchange fell 1000 points in one day. At one point, the Dow dropped 481 points in six minutes and then recovered 502 points just 10 minutes later."

"And that's bad, I take it?" said John.

"If it were up to machines, no, they would rapidly self-adjust, but as Halwell has always said, the market is not run at incredible speeds by machines, it is run at panicked speeds by human beings and human beings can panic a great deal in a matter of moments. People would be trying to yank their money. The value of world currencies would collapse.

"Have you ever seen 'It's a Wonderful Life,' John?"

"What, that schmaltzy American thing?"

"Yes, there's a run on the bank in that where everyone wants their money out of the bank because they think that the bank is running out, and it nearly causes the bank to collapse. And the protagonist, played by the inimitable Jimmy Stewart, he worked with us during the war, you know has to explain how money in a bank isn't just sitting in a vault, it's leant out to people and business and without that, everything grinds to a halt.

"Do you understand now, John?"

"Yes." It was staggering in its magnitude.

Halwell was led out. Her face and hands had been cleaned up, but her hands were bound behind her with a bar so that they couldn't touch. Her legs were in manacles.

"Good-bye, Mycroft, Sherlock. I know you won't visit. Mycroft can't—to be consorting with someone who is practically a traitor and a terrorist, and Sherlock won't because I'm a criminal, and worse, I'm a criminal who got caught."

"I'd visit," said John, quietly.

"Oh, you really do care, don't you? Care for my brothers, John. They'll need it, I think. And anyway, you'll never be able to visit. Trial by jury doesn't really apply here. Mycroft's going to be lucky to keep his job if he doesn't clean this up. I'll be on a plane out of England in two hours. I probably won't even be in Europe in four.

"What will you tell Mummy and Daddy, Mycroft?"

"That there was an incident and you won't be in touch for a long time. I will do everything in my power to protect them. It will break Mummy's heart. You have no idea how hard it was for her to send you away."

"But she did it just the same, didn't she?"

Suddenly Sherlock took off his scarf and flung it at her feet.

"My scarf…" Halwell said, surprised. "You've worn it all this time?" And for just a moment there was a sadness and a slightly pleading look in her eyes. And then it was gone, "Mes frères, nous ne sommes rien—l'oeuvre c'est tout."

Mycroft nodded and she was roughly pushed into a waiting black car with tinted windows. They watched as it sped away.

"Is it secure?" Sherlock asked quietly.

"Bullet proof, fire proof, laser locks that will not open from the inside unless there is an accident. I've attached a tracking device to the car, the driver and to her."

"She'll find it."

"Oh, I know. It's only until I can get one inserted subcutaneously, preferably implanted so she won't be able to remove it…but I don't want to hurt her permanently. Bone injury might calcify and there's the potential for tumors in organs."

"Why didn't you do it before?"

"I haven't done it to you either," Mycroft snapped. "Believe what you will of me, Sherlock, I care about you both."

Sherlock nodded curtly and started to walk away. John went to follow, unsure of what comfort he could offer his friend. Half dragging, half carrying Harry to bed when she staggered home seemed so small compared to this.

"Leave him, John. They were so very close once upon a time. Like twins. It was a world that even I couldn't enter into. But then we grow up.

Go to a hotel tonight, John. Check into any hotel you like, toiletries and a change of clothes will be waiting for you. Let him be for now."

Before he walked away John picked up the scarf, folded it gently and put it in his pocket.

Despite Mycroft's warning John couldn't sleep and found that he didn't want to stay in the hotel room. He needed to go back to 221b. His friend needed him.

He heard the music as he climbed the stairs. It was one of the most melancholy sounds he'd ever heard.

Mycroft sat in Sherlock's chair playing the viola, while Sherlock sat at his knees playing his violin. Their eyes were shut as they both swayed in time. The music was haunting and incredibly sad. At a pause in the music Sherlock leant his head briefly against his brother's knee.

Epilogue

6 months later

John came in from work to find Sherlock at the window, a piece of paper in his hand which hung limply by his side.

"Sherlock?"

"Moriarty's dead."

"What? How do you know?"

In reply, Sherlock thrust the paper at him. It was pale blue and looked handmade. The script was fine and neat. There was a faint scent of flowers and spices. John's eyes went rapidly to the signature:

**Love,**

**Halwell**

He scanned back up to the top.

**Dearest Sherlock,**

**I hope you are well. I send you glad tidings. Moriarty is dead! Think of it as a present. I thought of sending you the head as proof, but that would be so messy, and I knew it would upset John. So I have hidden it for you and Mycroft** **to find. It will be just like the paperchases and scavenger hunts we had as children. You'll have to work together though-to be a family again! And I will be waiting for you at the end. Tell John that X has converted to Y.**

Beneath the words there was a string of characters.

"What are these, Chinese?"

"No, Japanese. You can tell by the kana. As you know much complex kanji is made up of ideograms or simpler kanji. Take the symbol for boy, add the one for cap and you have the kanji for student. She's changed one of the ideograms in each of these kanji to make it mean something else. But I don't know what the new meaning is supposed to be. I don't speak Japanese.

"And Mycroft received a similar letter with another clue. We've arranged to meet this evening at his club to try and figure it out. Will you come?"

"Of course, but I doubt I will be much good."

"You are always good, John. That's why I need you. Why we need you. I'm beginning to think that none of the Holmes siblings are very good."

"You know that's not true."

Sherlock smiled wanly.

"But how did she do this? Isn't she locked up in some prison somewhere?"

"She escaped. A week ago. I didn't want to tell you. Mycroft and I believe that she may have engaged Moriarty's help to escape. He probably thought that it would be a coup to have my sister working for him. But of course, she doesn't work for anyone. Heads have rolled for this. Mycroft has seen to that."

"Sherlock, how did you get this letter? Isn't the house watched?"

"It was on the windowsill of my bedroom this morning. Likewise Mycroft's. There are always blind spots in surveillance. Wetware…

"The game, John, is on…"

John thought he had never heard anyone sound so sad in his life.

* * *

**Oh, I really so wanted to have their father work for UNIT, but it was too absurd for the tone of the story, but I did throw Doctor Who in there for fun. **

**I would love some feedback on the Britishism. Thanks to Langdale about Bethnel Green.**

**All I wanted to do was to see if I could actually write a mystery, even if it was stolen from the canon. And as the story poured out, I broke all my own rules. I created an OC Holmes sibling and then I had her talk too much, and then I made the mystery too short, and the dénouement too long, and gave answers for some of the questions that should remain enigmatic. Dumped some of my own brain into it for good measure (and you may think it's too long an explanation of too many things, but it pays off) but she is not Mary-Sue. I hope I am nothing like her. I hope that the words that she says help John understand Sherlock and Mycroft better. No more slash than the show and sideways from that it's not really edited as well as I would like but I have to get it off my desk to move on to other things. I want to do NaNoWriMo with friends next week, and I wouldn't be able to if I didn't finish this. This also gives me an ending to another of my unfinished pieces, so hopefully I can clear all these up before the 1****st****.**

**Sorry for the Basil Exposition from Mycroft and Sherlock about her crime. I couldn't figure out any other way to explain what I'd meant, and really, isn't that part of why John's there, to let Sherlock or Mycroft explain the crime? Hope I haven't made it too lecturely. I do work in the financial industry, but in marketing and way, way down the ladder, far away from the traders. The information about the hidden servers, the trading algorithms, the May 6****th**** Flash Crash, the times of the markets and the speed of the London Stock Exchange trading is all as true as I can make it. I have not heard that the Hong Kong Stock Exchange is about to use the same system. The information about kanji is also as true as I can make it, but I'm not sure if ideograms can be changed to significantly alter the meaning of several kanji so that it would actually form new words, but I know it has been done at least once. I've never taken probability, but that's my understanding of it, with a little help from the Internet. I also know nothing about how the servers might be guarded.**

**This came out of an article I read some months ago in the course of my work on the Flash Crash, and when I was looking up that article to refresh my memory I learned that the London Stock Exchange had just announced the fastest algorithm on October 11****th**** and then Mandelbrot died, so it seemed destined to be written. **

**I do in fact record things without knowing that I've recorded them. As I write and re-watch the series I hear lines that I've used without consciously remembering them in the show, like the one about choosing sides. I also remembered a remarkable amount of 'The Red Headed League" despite having not read it for over 20 years. I dream in color.**


End file.
